Torque converter type automatic transmissions are used extensively by the automobile industry in motor vehicle applications. These torque converters operate to hydraulically couple the torque output of the engine to the gear box of the transmission. Lock-up clutches are used in torque converters to improve fuel economy at cruising speeds by reducing the power losses caused by the inherent slippage in the hydraulic coupling. Lock-up clutches are designed to engage above a predetermined minimum vehicle speed and effect a direct mechanical coupling of the engine and the transmission gear box. This results in a bypassing of the hydraulic coupling and an elimination of the slippage in the automobile drive train.
Conventional lock-up clutches have three main components; a pressure plate, a front cover and a friction ring. The mechanical coupling effected by the clutch is achieved by forcibly extending the pressure plate of the clutch until it squeezes the friction ring between itself and the base plate of the front cover. An example of a conventional torque converter lock-up clutch can be found in Mikel U.S. Pat. No. 4,289,048.
An exploded view of the major components of a conventional torque converter manufactured by General Motors Corp., Detroit, Mich. (GM), is shown in FIG. 1. The converter includes a lock-up clutch having a front cover 2, a pressure plate 4 and an annular friction ring 6 bonded to the pressure plate surface 8 facing the front cover 2. The base plate 10 of the front cover 2 has a friction surface 12 for engaging the bonded friction ring 6. The torque converter further includes an impeller 14 which hydrokinetically drives a turbine 16. When assembled, the turbine 16 is connected to the output shaft (not shown) of the converter and the impeller 14 is welded to the front cover 2 which is in turn connected to the engine crankshaft (not shown). Thus, the torque output of the engine is transmitted to the impeller 14 by the front cover 2 and then through the transmission fluid to the turbine 16 and the automobile drive train.
FIG. 2 is a partial cross sectional view of the GM converter clutch showing the clutch in its engaged position. Referring to FIG. 2, the pressure plate 4 which is connected to the turbine 16 has been extended outward from the turbine 16 until the bonded friction ring 6 has contacted the base plate friction surface 12. This effects a direct mechanical coupling of the front cover 2, pressure plate 4 and turbine 16 resulting in a bypassing of the hydraulic coupling and an elimination of the slippage in the drive train. This view also shows that the GM front cover 2 has a rounded inner corner 28 at the intersection of the base plate 10 and the side wall 23.
In conventional applications, the friction ring in the lock-up clutch is made of a heat and wear resistant material. Examples of such prior art material can be found in H. F. Arledter et al U.S. Pat. No. 3,270,846. The ring in conventional applications is either bonded to one of the clutch surfaces or floats freely in between them. Floating friction rings, because of their dual friction surfaces, have longer lives and provide better sealing within torque converters. Conversely, bonded friction rings, which only have a single friction surface, cannot provide these additional benefits. Therefore, when rebuilding torque converter clutches which originally employed bonded friction rings, it would be advantageous to replace them with floating rings. However, these bonded applications are not generally retrofitable with floating friction rings because their front covers do not have squared ring receiving surfaces.
Conventional floating rings are flat annular disks and therefore require that the inside corners of the front cover be square in order to properly interact with the outer edge of the ring. Without the squared corners, the ring cannot be properly piloted and centered within the main bore of the front cover. Therefore, when retrofitting floating rings into bonded applications, machining is necessary to remove the interfering surfaces which exist at the periphery of the base plate of the front cover in order to create a squared receiving surface for the ring. However, this machining cannot be accomplished without significant damage to the front cover and, therefore, the old bonded ring must be replaced by a new bonded ring having the same disadvantages.
FIG. 3 is a diagrammatic cross sectional view of a bonded application clutch 40 retrofitted with a conventional flat floating friction ring 30. This figure is an illustration of the type of problem which the preferred embodiment is designed to eliminate. Referring to FIG. 3, the pressure plate 32 has engaged the friction ring 30 but the base plate 34 of the front cover 36 has an annular interfering surface 35 extending outwardly at its periphery which prevents the floating friction ring 30 from engaging the base plate friction surface 33. Therefore, in order to install the floating friction ring 30 in this type of converter, it is necessary to machine the front cover 36 to remove the interfering surface 35 to allow the friction ring 30 to sit squarely within the bore 37 of the front cover 36 thereby properly engaging the base plate friction surface 33.
Replacement of an old bonded ring with a new one involves removing the old clutch surface and adhesive by mechanical or chemical methods, preparing the metal surface to receive the new ring, applying adhesive and adhering the ring to the clutch surface through the application of heat and pressure, (several examples of bonding frictional materials to metal surfaces can be found in the Arledter patent). On the other hand, retrofitting with a floating friction ring would only require the removal of the old ring and would eliminate the processing associated with adhering a new ring. Therefore, if it were not for the aforementioned problems associated with the interfering surfaces on the base plate, retrofitting a bonded application with a floating friction ring would involve less processing of the clutch parts and result in time and money savings.
Accordingly, it is the broad object of the present invention to provide a contoured floating friction ring for general use in torque converter lock-up clutches.
A more specific object of the invention is to provide a contoured floating friction ring for use in retrofitting conventional bonded ring torque converters.
Another object of the invention to provide method for custom fabrication of the contoured floating friction ring of the invention.
A still further object of the invention is to provide a floating friction ring and method of fabrication which effect economies in materials and retrofitting applications thereof.